Microorganisms are highly adaptable to surrounding environments, which allows cultures to colonize nearly any environment. Some microorganism cultures are resistant to very recalcitrant pollutants including, for example, polychlorinated biphenyls, heavy metals, and hydrocarbon fuels.
Bacteria have been isolated from fuels, fuel storage tanks, pipelines, aircraft wing tanks, and offshore oil platforms, in which the bacteria may cause problems such as tank corrosion, fuel pump failures, filter plugging, injector fouling, topcoat peeling, engine damage, and deterioration of fuel chemical properties and quality. Extensive microbial growth and biofilm formation within the fuel, fuel tanks, or fuel lines may also lead to costly and disruptive damage to fuel systems. These besides have the ability to metabolize hydrocarbons and thrive in the environments containing toxic compounds (i.e., aromatic hydrocarbons), low nutrient availability (metal ions, phosphorus, etc.), and low water amounts.
Normally, bacteria metabolize alkanes via oxidation. However, the genome of bacteria adapted to grow in in jet-fuel systems and petroleum oil field (such as P. aeruginosa) encodes two membranes bound alkane hydroxylases (alkB1 and alkB2), essential electron transfer proteins, ruberdoxins (RubA1, RubA2), and FAD dependent NAD(P)H2 ruberdoxin reductases, which oxidize a terminal methyl group of the alkanes into a primary alcohol group via alkane hydroxylases aided with electron transfer proteins. The primary alcohol group is oxidized to an aldehyde and a fatty acid and followed by β-oxidation to generate acetyl-CoA, the entry molecule for the citric acid cycle.
The role of membrane proteins and cell membrane is crucial in regulating cell homeostasis. One class of membrane proteins, encoded by the opr genes, includes substrate specific porins that transport molecules from the extracellular environment into the cell. Two such porins, OprF and OprG, are involved in the transport of aromatic hydrocarbons and other hydrophobic small molecules into the cells. Fuel contains aromatic and cyclic hydrocarbons, which are toxic to the cell. Also, fuel can capture heavy metals and other molecules during transport and storage, which may also affect bacteria. It has been proposed that membrane proton antiporter-pumps or efflux pumps of the resistance-nodulation-division (“RND”) family function in the extrusion of toxic compounds including antimicrobials, organic solvents, and heavy metals.
Despite the current understanding of bacterial growth in fuels, there remains a need for methods of controlling and/or preventing such bacterial growth and other microbes that are responsible for biodeterioration of the fuel.